1. Field of the Invention
This invention pertains to spinal stabilization surgical procedures and apparatus for performing such procedures. More particularly, this invention pertains to an apparatus and method for implanting a fusion spinal implant between two vertebrae.
2. Description of the Prior Art
Chronic back problems cause pain and disability for a large segment of the population. In many cases, chronic back problems are attributed to relative movement between vertebrae in the spine.
Orthopedic surgery includes procedures to stabilize vertebrae. Common stabilization techniques include fusing the vertebrae together.
Recently, spinal implants have been developed to facilitate successful fusion of vertebrae. In such procedures, a bore is formed between opposing vertebrae to be fused. An implant, commonly containing bone growth-inducing material such as harvested bone chips, is placed within the bore.
In order to enhance the successful procedure, a bore should be formed centrally between the vertebrae such that the bore cuts equally into both vertebrae. Also, from time to time, it is desirable to place two implants within the same disc space. In such procedures, it is desirable that the vertebrae be spaced apart by a minimum spacing sufficient to prevent the implants from contacting one another during the implanting procedure. In the prior art, numerous methods have been disclosed for performing spinal stabilization procedures.
A spinal implant and stabilization procedure is taught in U.S. Pat. Nos. 5,015,247 and 5,484,437 both to Michaelson, dated May 14, 1991 and Jan. 16, 1996, respectively. That patent teaches a threaded spinal implant as well as a method of implantation including certain tools to form a bore into which the implant is threaded. An implant and surgical method are also shown in U.S. Pat. No. 4,961,740 to Ray, et al., dated Oct. 9, 1990, as well as U.S. Pat. No. 5,026,373 to Ray, et al., dated Jun. 25, 1991. The latter patent teaches preparing a bore for the implant by drilling over a pilot rod.
In addition to cylindrical threaded implants such as those shown in U.S. Pat. No. 5,015,247, implants may take on different geometries, including non-cylindrical implants such as those shown in U.S. Pat. No. 5,609,636 dated Mar. 11, 1997. Also, conical implants have been suggested, where the conical implants have a conical angle approximating a desirable lordosis between the opposing vertebrae.
In surgical procedures involving implants, it is desirable that the surgical procedure be performed accurately to ensure central positioning of the implant within the disc space between the opposing vertebrae. U.S. Pat. No. 5,489,307 to Kuslich, et al., dated Feb. 6, 1996, teaches a plurality of instruments and a surgical method for preparing a bore for receiving an implant. That procedure results in accurately positioning an implant centrally between the opposing vertebrae while avoiding certain disadvantages with other prior art techniques as discussed more fully in the ""307 patent. Unfortunately, the method and procedure of the ""307 patent requires a large number of instruments which must be accurately selected and manipulated.throughout the procedure. It is an object of the present invention to provide an apparatus and method for performing spinal stabilization using a reduced number of instruments in order to simplify the procedure without sacrificing the accuracy achieved with the procedure of the ""307 patent. Furthermore, it is an object of the present invention to provide a surgical procedure that can be performed posteriorly, anteriorly, laterally, or as a laparoscopic procedure.
According to the preferred embodiment of the present invention, an apparatus and method are disclosed for implanting a spinal fusion implant into a disc space separating a first vertebra and a second vertebra. The method comprises inserting a distal end of a rigid centering guide into the disc space. The guide extends along a longitudinal axis from a distal to a proximal end. The guide has a first external guide surface with a predetermined geometry. A drill guide is placed against the centering guide. The drill guide is adapted to axially guide a drill. The drill guide has an external guided surface which is shaped complementary to the external guide surface of the centering guide. The external guide surface and the guided surface are mutually nested with the guided surface sliding against the external guide surface along a path of travel parallel to the longitudinal axis of the centering guide. The drill guide is slid toward the vertebrae with the guide surface and the guided surface maintaining movement of the drill guide along the desired path of travel.